This video is about the enzymes that, for me, first turned cells into little toy chests full of delightful tiny gadgets.

All of the mechanical things that our bodies do, like keeping other things out, or seeing, can be described by somewhat abstract functions. For example, ‘the skin makes a protective sheet’ or ‘the lens focuses light’. But then all of those abstract functions can be broken down again into mechanical motions of the small molecules inside the cells, complete with hinges and springs, making them seem tangible once more, at least to my mechanism-oriented mind: The outside of each skin cell is littered with little molecules that hold on to the same types of molecules on the next cell in a strong handshake, forming a tight, grime-proof layer, while lens cells pack hundreds of copies of a single type of protein up tight against each other, forming almost a crystal, and then jettison all of things in the cell that would scatter light, like DNA or mitochondria, in order to let light pass cleanly through the cell.

This story in this video is about a problem that all living things have — how long and thin DNA is, and how easy it would be to get it all tangled. Not only is there a huge amount of DNA in each cell (around two meters in each human nucleus, for example), but also every time a cell divides into two, the two strands of all of that DNA have to be untwisted from each other to be copied. Think about pulling the fibers of a length of twine apart; the wound end gets tighter and tighter and then twists up on itself, making it impossible to move forward. Thankfully there are these little enzymes, called topoisomerases, that are there to iron out the wrinkles.